docs: def space_labels(document):
      """Ensure space around bold compound labels."""
      for label in document.xpath('.//bold'):
          # TODO: Make this more permissive to match chemical_label in parser
          if not label.text or not re.match('^\(L?\d\d?[a-z]?\):?$', label.text, re.I):
              continue
          parent = label.getparent()
          previous = label.getprevious()
          if previous is None:
              text = parent.text or ''
              if not text.endswith(' '):
                  parent.text = text + ' '
          else:
              text = previous.tail or ''
              if not text.endswith(' '):
                  previous.tail = text + ' '
          text = label.tail or ''
          if not text.endswith(' '):
              label.tail = text + ' '
      return document